Engines utilize several methods to control the amount of heat transfer from the engine block to the vehicle surroundings. Engine coolant passes through jackets in the engine to carry heat from combustion to the radiator. At the radiator, heat is transferred to surrounding air. The amount of heat transfer can be adjusted by varying either or both of the amount of airflow across the radiator (e.g., via a fan), and by varying the amount of coolant flow through the engine.
In one example, electronically controlled actuators are used to provide variable airflow (e.g., via a variable speed fan) and variable coolant flow (via a variable speed coolant pump). The two actuators are controlled based on operating conditions in an attempt to provide increased fuel economy and optimal temperature control. Such a system is described in SAE 2001-01-1742.
The inventors herein have recognized a disadvantage with such an approach. Specifically, at least two separate electrical actuators are required to independently control the airflow (e.g., fan) and the coolant flow (e.g., coolant pump). This adds additional cost compared with mechanical engine coolant pumps that are simply driven proportional to engine speed.
Nevertheless, the inventors herein have also recognized that having the ability to control the engine coolant and fan speed independent of engine speed does offer potential fuel economy gains.